In the conventional cylinder lock devices, the proper key can be rotated to the locked position or the unlocked position in a key cylinder having tumblers which are engaged with grooves formed within a case. In a conventional steering lock device that prevents the rotation of the key cylinder by means of the tumblers engaged with the grooves within the case, there is a danger that unauthorized unlock will occur as a result of damage to the tumblers. Thus, for example, as disclosed in Japanese Patent Disclosure No. 1-315569, a free-turn type cylinder lock has been proposed, wherein a key cylinder is designed, so that it can be freely rotated against an unauthorized attempt to unlock when rotational force is applied to the key cylinder. This cylinder lock is provided with a sleeve rotatably arranged in a case and the key cylinder rotatably supported within the sleeve.
When the proper key is inserted into the key cylinder, tumblers within the key cylinder are disengaged from grooves formed within the sleeve, and thereby the key cylinder can be rotated relative to the sleeve, so that a sliding ring engages with a lock-piece operating member to actuate the lock. If a foreign key is inserted into the key cylinder, as the key cylinder is kept in the condition that it is engaged with the sleeve by means of the tumblers, the key cylinder rotates together with the sleeve. Thus, the lock-piece operating member is prevented from rotating, and thereby the lock device cannot be actuated.
In case a foreign key is used in this kind of free-turn type cylinder lock, the key cylinder freely rotates. Therefore, since excessive rotation force that might break down the tumblers cannot be given to the lock, significant resistance can be given to the lock against damage or destruction.
However, the lock device disclosed in Japanese Patent Disclosure No. 1-315569 cannot be applied to a steering lock device. In order to apply the free-turn type cylinder lock to a steering lock device, it is further necessary to develop the technology concerned.
Accordingly, it is an object of the present invention to eliminate the aforementioned disadvantage and to provide a steering lock device with a key cylinder which is capable of freely rotating without fail in case of an unauthorized attempt to unlock.